The efficient functioning of the hip joints is extremely important to the well being and mobility of the human body. Each hip joint is comprised by the upper portion of the upper leg bone (femur) which terminates in an offset bony neck surmounted by a ball-headed portion which rotates within a socket, known as the acetabulum, in the pelvis. Diseases such as rheumatoid- and osteo-arthritis can cause erosion of the cartilage lining of the acetabulum so that the ball of the femur and the hip bone rub together causing pain and further erosion. Bone erosion may cause the bones themselves to attempt to compensate for the erosion which may result in the bone being reshaped. This misshapen joint may cause pain and may eventually cease to function altogether.
Operations to replace the hip joint with an artificial implant are well-known and widely practiced. Generally, the hip prosthesis will be formed of two components, namely: an acetabular, or socket, component which lines the acetabulum (hereinafter an acetabular component); and a femoral, or stem, component (hereinafter the femoral component) which replaces the femoral head. During the surgical procedure for implanting the hip prosthesis the cartilage is removed from the acetabulum using a reamer such that it will fit the outer surface of the acetabular component of the hip prosthesis. The acetabular component of the prosthesis can then be inserted into place. In some arrangements, the acetabular component may simply be held in place by a tight fit with the bone. However, in other arrangements, additional fixing means such as screws or bone cement may be used. The use of the additional fixing means help to provide stability in the early stages after the prosthesis has been inserted. In some modern prosthesis, the acetabular component may be coated on its external surface with a bone growth promoting substance which will assist the bone to grow and thereby assist the holding of the acetabular component in place. The bone femoral head will be removed and the femur hollowed using reamers and rasps to accept the prosthesis. The femoral component will then be inserted into the femur.
In some cases, a femoral component of the kind described above may be replaced with components for use in femoral head resurfacing or for use in thrust plate technology.
Hip replacements do not have an infinite life. A major factor influencing the life expectancy of a prosthetic implant is wear of the articulating surface. The pressures acting on the implant contact surface can be of the order of 30 MPa/cm2 during normal function. Over time wear debris is formed as the components of the hip replacement articulate against one another. These particles can cause osteolysis and adverse tissue reactions which will lead to loosening of the component and reduce implant life.
Currently the average life expectancy of a hip prosthesis is between 10 and 15 years. Where the implant has been placed in an elderly patient this period may be sufficient. However in a young patient, it is likely that one or more revision operations will have to be performed during the lifetime of the patient. One problem associated with these revision operations is that it is more difficult to get a tight fit between the replacement acetabular component and the pelvis due to further degradation of the bone.
In the case of the aforementioned revision operations, where there has been damage to the pelvis due to arthritis or in the case of patients suffering from dysplasia (shallow hip sockets), additional fixation means may be required to hold the acetabular component in place. In some arrangements, a hook feature may be included to hook around the edge of the pelvis adjacent to the obturator foramen.
Various proposals have been made with a view to providing improved acetabular component prosthesis which are particularly suitable for use with patients that are undergoing revision surgery, those whose pelvis is damaged or those who suffer from dysplasia.
RU2201174 describes an acetabular component which has a plurality of leaflets extending from the edge of the acetabular component which each include a hole through which fastening screws can be passed into the pelvic bone. The leaflets are bendable to conform to the shape of the pelvis. A hook is also included which is hammered into the bone tissue.
In EP0605368 a replacement acetabular component which is delimited by a circular flange is described. The flange is provided with a plurality of recesses for engaging therein radially extending elements which can be screwed to the pelvis. As this prosthesis has several separate elements, it can be difficult to fit.
WO95/15132 discloses an acetabular component which is held in place by screws inserted into the bone through the cup of the component. The cup is delimited by a flange which has holes therethrough which allows additional screws to be used. The acetabular component described in WO01/70141 is also held in place by means of screws placed through the side of the cup.
An alternative arrangement is described in WO99/22672. Here in addition to the cup of the acetabular component being held in place by means of screws which are passed through the wall of the cup, an extension through which screws may be placed is provided to enable the cup to be fitted in deficient acetabulae. The extension may be provided at selected angles depending on the acetabular defect which is to be treated. Alternative arrangements are described in WO03/013397 and US2003/0171818.
One problem associated with arrangements in which the cup is held in place by screws located through the cup is that interaction between the head of the femur may cause wear. It will be understood that the presence of screw holes in the cup disrupts the articulating surface which is disadvantageous particularly where the interface between the articulating components is metal/metal.
In FR2819172 a replacement acetabular component is described which includes a hook to engage the pelvic aperture and a rigid fixing lug extending from the component and angled thereto such that in use, when the component is placed in the orientation proscribed by the location of the hook, screws can be passed through holes in the lug to anchor the component in place. However, since the angling of the lug means that the acetabular component is orientation specific, separate components must be manufactured for the left and right side which increases the manufacturing costs.
An alternative arrangement is described in U.S. Pat. No. 6,620,200. The cup comprises a hemispherical part which is extended over substantially half the circumference of an equatorial edge of the hemispherical part and is defined by a plane inclined to the equatorial plane. The acetabular component is fitted with two extensions through which screws can be passed into the iliac. An obturator hook is located at a position diametrically opposite to a point situated at the center of the interval between the extensions.
While these acetabular components all go some way to providing an arrangement which can be readily attached to the pelvis, particularly in revision operations, in the treatment of dysplasia, or in an otherwise deficient pelvis, they suffer from various disadvantages and drawbacks. The modular systems can be expensive to manufacture and difficult to fit. Many of the systems only allow for short screws to be used due to the angle in which they are inserted into the bone and thus the support for the acetabular component may not be sufficient for prolonged use. Finally, the components may be orientation specific to only the left or right acetabulum thereby increasing the costs of manufacture. In some arrangements, the insertion of the screws may cause the acetabular component to be pulled out of alignment.
It is therefore desirable to provide an arrangement which overcomes the above-mentioned disadvantages. This can be achieved by the provision of an acetabular component which enables a fastening means to pass through a flange extending from and integral with the acetabular component in both a left-handed and right-handed manner such that the cup can be used in the left or right side of the pelvis.